1. Field of the Invention
The invention relates to an information obtaining apparatus used for a vehicle. More particularly, the invention relates to an examination concerning identification information.
2. Description of the Related Art
A tire inflation pressure alarm apparatus is widely known, which determines whether a tire inflation pressure is an abnormal value based on a radio signal including a measurement value of the tire inflation pressure, and which issues an alarm when the tire inflation pressure is determined to be an abnormal value. Such a tire inflation pressure alarm apparatus includes a transmission device which is provided in each tire, and a reception device which receives a radio signal transmitted from the transmission device.
The transmission device measures a tire inflation pressure, and wirelessly transmits the measurement value and tire identification information ID for identifying the tire. The reception device receives the radio signal transmitted from the transmission device, and determines whether an abnormality has occurred in the tire inflation pressure. The tire identification information ID for each of all the tires of the vehicle is registered on the memory of the reception device in advance. The reception device determines whether the tire inflation pressure information included in the received radio signal is for the host vehicle, by comparing the tire identification information ID included in the received radio signal with the tire identification information ID registered on the memory. The tire identification information ID is registered on the memory when the tire is attached to the vehicle.
For example, Japanese Patent Laid-Open Publication No. JP A 2000-233615 discloses a technology in which communication is performed for a predetermined set time, and the identification information which is most frequently received is registered as the identification information transmitted from a transmission device provided in a tire of a host vehicle. Japanese Patent Laid-Open Publication No. JP A 09-210827 discloses a technology in which a reception device registers the initially received identification information for each of four wheels, as the identification information transmitted from a transmission device provided in each tire of a host vehicle.
In the above-mentioned technologies, generally, an output from the transmission device is set to have sufficient strength with respect to the reception sensitivity of the reception device, in order to perform reliable communication between the transmission device and the reception device using a radio signal. Therefore, the reception device may receive a radio signal from a transmission device provided in a wheel attached to another vehicle.
After the identification information from the transmission device is registered when the tire is attached to the vehicle, it is necessary to perform an examination of whether the identification information corresponding to the attached tire is registered properly (hereinafter, this examination will be referred to as an “examination concerning the identification information”). However, when the examination concerning the identification information is performed at a place, e.g., a vehicle production plant, where many vehicles are densely placed, there is a high possibility that the reception device receives a radio signal transmitted from a transmission device mounted in another vehicle. When the examination is attempted to be performed concerning the identification information from the transmission device provided in the host vehicle, the examination may be accidentally performed concerning the identification information from the transmission device mounted in the other vehicle. This causes a problem that the examination concerning the identification information cannot be performed accurately.